1. Field of the Invention
The present invention relates to a method for vertically and continuously casting beryllium copper alloys. More particular, the invention relates to a method for vertically and continuously casting beryllium copper alloys having both excellent mechanical strength and excellent processability, in which a crystalline structure consists substantially of isometric crystals.
2. Related Art Statement
In conventional methods for vertically and continuously casting the beryllium copper alloys, in order to make the crystalline structure of the copper alloy finer, an agent for making crystals finer (hereinafter referred to as "crystal refiner") is used, a casting temperature is lowered, or a melt is stirred.
However, the crystal refiner poses contamination of the melt, and there is also a problem that no appropriate crystal refiner cannot be found depending upon an alloy composition.
Although decrease in the casting temperature has a merit that crystal nuclei formed are not dissolved into the melt again, it causes troubles such as clogging of a nozzle, and also poses problems from the standpoint of the quality that internal defects such as inclusion and residual pores are increased.
On the other hand, an electromagnetically stirring method has problems in that an installation cost is high, and internal defects such as inclusion, residual pores and the like are likely to increase from the standpoint of quality.
In order to continuously cast a beryllium copper alloy, for example, a casting apparatus as shown in FIGS. 1a and 1b is conventionally used.
In FIG. 1a, a reference numeral 1 is a tundish. A melt 2 inside the tundish 1 is poured into a mold 5 through a nozzle 3 fitted to a bottom of the tundish 1 and an opening 4 of the nozzle 3. A reference numeral 6 is a cast ingot extracted from the mold 5, and a reference numeral 7 is a cast ingot-extracting member for supporting the cast ingot 6 and leading it downwardly. A reference numeral 8 is a flow rate-regulating mechanism for the nozzle. This mechanism is located in the tundish, and regulates the flow rate of the melt to be poured into the mold 5 through the nozzle 3 by adjusting an opening degree of a melt introducing opening defined between an outer peripheral portion 8a of the regulating mechanism 8 at the lower end and a melt-introducing opening 3a of the nozzle 3. FIG. 1b is a sectional view of the nozzle in FIG. 1a along a Ib--Ib line.
The method for continuously casting the beryllium copper alloy by using this casting apparatus has the following problems.
That is, although the casting needs to be effected at low temperatures to obtain the isometric crystals, the low temperature casting is likely to cause clogging of nozzle 3. More particularly, even when the regulating mechanism 8 is opened in the initial stage of the casting, the static pressure of the melt 2 is not applied to the entire interior of the nozzle 3, and the flow amount of the melt through the nozzle 3 is small. Accordingly, the stream of the melt is likely to be cooled at the initial stage due to removal of heat through the nozzle 3, so that the nozzle 3 is likely to be clogged. On the other hand, if the casting temperature is elevated to prevent clogging of the nozzle, a temperature gradient between an outer shell portion and an interior portion of the melt poured into the mold 5 becomes greater. As a result, columnar crystals among the crystals of the beryllium copper alloy predominantly grow along the temperature gradient, so that the resulting crystal structure consists essentially of a columnar crystals and mechanical properties such as mechanical strength and processability are deteriorated.
Therefore, beryllium copper alloys having great mechanical strength and excellent processability in which the crystalline structure consists essentially of isometric crystals cannot be obtained by the conventional method for vertically and continuously casting the beryllium copper alloy.